refactor: general architectural cleanup and bug fixes

internal/database/migrations/006_add_jikan_cache.sql

@@ -1,6 +1,9 @@
+-- +goose Up
 CREATE TABLE IF NOT EXISTS jikan_cache (
     key TEXT PRIMARY KEY,
     data TEXT NOT NULL,
     expires_at DATETIME NOT NULL,
     created_at DATETIME NOT NULL DEFAULT CURRENT_TIMESTAMP
 );
+
+-- +goose Down